Cooling means for gas turbogenerators



S. A. KANE COOLING MEANS FOR TURBOGENERATORS Filed Dec. 14, 1948 May 23, 1950 Attorney Patented May 23, 1950 COOLING MEANS FOR GAS TURBO- GENEBATORS Saul Allan Kane, Washington, D. C. Application December 14, 1948, Serial No. 65,261

4 Claims. (CL 290-2) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) This invention relates generally to the art of cooling the generator of a turbogenerator system.

It is well known that the efficiency of a generator may be increased by providing adequate cooling therefor. This improvement in eiiiciency is partly a. result of decreased size of a unit of given output Aand partly because of thinner and more eilicient insulation which may be employed on the turns of the windings of the rotor and stator parts. `It has therefore been the practice to provide an air blast directed along these windings so as to maintain the temperature thereof within the safe limits for the particular winding insulation used. In electrical generators of large power it has been the practice to provide a separate blower fan which directs a blast of air into and around the windings. In some smaller capacity generators it has been the practice of some manufacturers to attach the blower to the rotor within the housing. According to the prior art devices a. turbogenerator has consisted of three portions, the turbine, the generator and the cooling fan and duct assembly. When a prime mover other than a turbine is used the problem of cooling necessitates the same three functional elements, as for example where an internal combustion engine is combined with a generator.

In this invention the third functional element is omitted and the function accomplished by a modification of the gas turbine. The combination herein disclosed is essentially a two element turbogenerator in which air blast cooling is nevertheless provided, resulting in increased space and power eiliciency.

It is an object of this invention to provide a vturbogenerator system in which the generator is 'wm become apparent to those skilled 1n the art as the disclosure is made in the following detailed description of a preferred embodiment of the invention illustrated in the accompanying figure by a longitudinal sectional view.

The figure shows an arrangement wherein any suitable type of generator, designated generally by the numeral I, is mounted in any desired manner adjacent to the intake end of a gas turbine,

generally indicated by the numeral 2, wherein the rotor of the generator is mounted on the same shaft 3 as the rotor of the turbine. The gas turbine 4 is mounted at the rear end of the shaft 3 and fastened thereto by conventional means to provide rotation of the shaft as the turbine rotor is driven. In the central region of the shaft 3 is located the air compressor 5, which is keyed to the shaft to rotate therewith and to be driven thereby. A plurality of combustion chambers are arranged annularly about the shaft between the compressor and the turbine, two of which are shown in section at 6 and 1, the arrangement being such that the compressor feeds compressed air into the respective chambers or combusters and the turbine receives the heated gases there from. The compressor housing is provided with suitable outlet nozzles as at 8 feeding the compressed gas into the combustion chambers, and is provided at the forward end thereof with an annulus 9 connecting with an outside source in the conventional manner by means of an intake duct I I. This duct terminates in a location suitable to draw combustion air from an external source to supply the needs of the system. It may be desirable to provide manually variable louvers may be provided a slight constriction in the diameter of the duct so that the air passing therethrough is subjected to decreased local pressure in the portion at I2.

Louvers 23 are shown in duct I3 whereby the amount of air drawn through the generator may be varied at will by manual adjustment or automatically in accordance with the cooling effect desired. As illustrated in the figure the louvers 23 are automatically controlled by the linkage members 21, simultaneously with the controlling of the fuel valve 23, which in turn is controlled by the governor 29. Where automatic feed control is required to maintain a constant generator speed the linkage members shown serve to open the louvers 23 in proportion to the opening of the feed valve 28, such that cooling air passing through the generator varies proportionally to the load on the generator and the opening of valve 28.

Connecting with the portion of the duct I2 there is provided an auxiliary air duct I3 which connects with the casing I4 of the generator I such that any air drawn into the compressor through the auxiliary duct Il passes through the casing Il. Suitable air inlets I are provided preferably at the forward end of the generator, and air passages are arranged through the generator adjacent to the windings and the brushes, the construction of these air passages being chosen to provide maximum cooling where the heat to be dissipated is greatest. Various modifications.

of the structure of the stator and rotor of the generator have been proposed for increasing the cooling effect of air passing through suchv a generator.

In the construction shown in the figure it is noted that the entire housing shown could be assembled in one piece with a common shaft 3 extending substantially therethrough, `or the shaft could be jointed as desired for convenience of subassembly. The housing is shown jointed for easier manufacture and could be jointed in any other convenient manner.

The turbine housing terminates in an exhaust annulus as at IB and an exhaust duct I1 is provided for carrying oif the emergent gases. Within the annulus I5 and secured to the housing is a bearing I8. A second bearing I9 is shown at the forward end of the generator and a third bearingr may be provided at the rear of the generator as illustrated at 2|. Other bearings may be provided in the event the shaft is jointed.

The fuel for heating the compressed gas is provided via the fuel pipes 22 preferably through a valve which may be controlled manually or automatically according to any conventional construction of gas turbines. The fuel is initially ignited by an electrical spark within the mixing cone 25 after the rotor has been turned up to driving speed. The gas turbine is shown comprising four stages of expansion, and the compressor having six stages, the number of stages in each case being variable according to the efficient design for turbines designed for various speeds of operation.

A starting means is illustrated at 26 for initially bringing the turbine rotor up to drivingl speed, and may consist of an electrical motor and gears or other driving means.

In accordance with the arrangement illustrated and described the compressor draws gas from an external source through the intake duct, and additional gas through the generator by way of the cooling ducts therein, mixes the two currents of intake gas and compresses the mixed gases, exhausting this compressed gas into the combustion chambers where a portion of the oxygen thereof is used for combustion of the fuel within the mixing cone and combustion chamber and the remainder thereof is used to cool the products of combustion to an acceptable limit, the heated emergent gases then exhausting through the turbine to drive the compressor and the generator attached thereto by the shaft 3. The fuel consumed serves to heat the intake gases not consumed in burning the fuel, so that compressed hot gases enterr the turbine and there give up energy to the turbine rotor.

The intake gas passing through the duct II is normally at ambient temperature but is heated by compression in the compressor 5.

The heat taken up by the air passing through the generator results in a very slight rise in temperature of the intake air entering the compressor which may result in slightly decreased compressor efficiency. This loss is much more than compensated by increased elciency in the whole system by elimination of power loss in a separate fan for cooling the generator. A considerable saving in weight especially of moving parts is also achieved which advantage is important in emergency service generator systems connected to power lines and which are started and brought up to full power output in a few seconds. The temperature of the generator is controllable by controlling the relative amounts of air entering by ducts II and I3, which may be done by controlling the opening of the louvers III or 2l or both. By mixing the gas from the ducts II and I3 in the annulus I2 and in the compressor the compressed air emerges from the compressor at uniform temperature.

In combined engine and generator sets previously known, where cooling air is circulated about or through the generator by means of an added fan assembly, the fan is connected to the engine shaft, directly or indirectly. In such systems the fan speed is proportional to the engine speed, regardless of the output of the generator, and regardless of the heat to be dissipated by the generator. The amount of heat to be'dissipated is primarily a function of the generator output, arising largely from internal electrical resistance. The cooling is consequently most important at the higher outputs and the cooling system must be designed to provide adequate cooling at maximum output. In many classes of service the generator is normally operating considerably below maximum output and the cooling provided is necessarily much more than adequate at the lower electrical output. For example, when one horsepower of energy is expended in cooling the generator and the useful output thereof is four horsepower a twenty percent loss results. Such losses represent a considerable factor in the overall economic efficiency of the machine for normal service in which much of the operation is at less than full capacity.

In this invention the volume of cooling air is made proportional to the volume of fuel fed to the combustors and hence to the electrical output. The power employed in cooling the generator thus remains substantially a linear function of the generator load and is consequently kept approximately at the minimum value for adequate cooling. The aforementioned exemplifled loss of 20 percent of the power produced in previous systems is therefore prevented and is restricted to a small part thereof, regardless of the power output of the generator. Normally not over one percent of the power produced need be employed for cooling, in contrast to the much larger losses inherent in prior devices.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood. that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

The invention described herein may be manufactured and used by or for the Government oi the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

l. Ina turbogenerator of the class disclosed the combination of a gas turbine comprising gas compressing, gas heating and rotary power absorbing elements; a shaft driven by said turbine; an in take duct connected to said compressing element; an electrical generator driven by said shaft and having therethrough cooling gas passages; means connecting said cooling passages to said duct;

governor means for said turbine operative in response to the load thereon; and valve means in said cooling passages operatively controlled by said governor means, whereby ambient gas is drawn through the cooling passages in proportion to the power output of the generator.

2. In a turbogenerator of the class comprising a gas turbine assembly driving an electrical generator, duct means connected to the gas turbine intake for drawing a fraction of the operating gas for said turbine from an ambient temperature source, further means for drawing the remaining fraction of said operating gas from a further ambient temperature source including further ducts through the generator arranged adjacent heated portions of said generator, means connecting the outlets of said ducts and said further ducts for mixing the gases therefrom, whereby all of said operating gas is preheated in proportion to the cooling of the generator, and means responsive to the rate of fuel consumption for varying said fractions of operating gas derived from said sources, respectively, whereby the operating temperature of the generator is controlled and the cooling eiect thereon is varied in proportion to the load on the generator.

3. An air cooled turbogenerator consisting of a gas turbine including compressor, combuster and turbine elements, a generator operatively connected to and driven by the turbine element, an intake air duct assembly constructed and arranged to draw a fractional portion of the intake air for the compressor element through the generator in cooling contact relation thereto, and turbine speed-controlled means for varying said fractional portion in accordance with turbine load.

4. A gas cooled turbogenerator consisting of a gas turbine including compressor, combuster, turbine and speed governor elements, a generator operatively connected to and driven by the turbine, an intake gas duct assembly constructed and arranged to draw a fractional portion of the intake gas for the compressor element through the generator in cooling contact relation thereto, valve means in said duct assembly controlling gas flow through the generator and linkage means operable by said speed governor element controlling said valve means to admit gas therethrough in proportion to the generator output.

SAUL ALLAN KANE.

REFERENCES CITED The following references are of record in the file oi this patent:

UNITED STATES PATENTS Number Name Date 1,239,647 Ver Planck Sept. 11, 1917 1,526,988 Keilholtz et a1 Feb. 17, 1925 1,778,036 Noble et a1. Oct. 14, 1930 1,916,329 Nordberg July 4, 1933 2,019,026 Spear et al. Oct. 29, 1935 2,149,516 Flamm Mar. '1, 1939 2,358,301 Brauns Sept. 19, 1944 2,444,415 Beeson July 5, 1948 FOREIGN PATENTS Number Country Date 5,734 Great Britain Mar. 16, 1899 

